1. Technical Field
This invention relates to a maintenance liquid suitably used for printers for ink jet recording.
2. Related Art
Ink jet printers have recently been commercialized as noiseless, high speed, and high resolution non-impact printers. As a solvent for an ink used for ink jet recording, an aqueous ink using water and a water-soluble organic solvent is mainly used in view of odor, safety, and the like. Also, although water-soluble dyes have heretofore been used as colorants for the ink to be used for ink jet recording, a change from the water-soluble dyes to pigments have been made in view of printing quality improvement, image robustness, and the like, and use of the pigments is being expanded. Further, there is a tendency that a content of the pigment in the ink is increased.
Under the circumstances, since the ink is discharged from a nozzle having a microdiameter of about 20 to 50 μm in the ink jet recording method, an increase in viscosity of the ink and generation of deposits tend to occur in the vicinity of the nozzle front end due to volatilization of a low boiling point solvent, separation of a colorant, aggregation, and the like, and defects such as disturbed print and nozzle clogging are caused in some cases. A cap for nozzle drying prevention and a cleaning mechanism for cleaning with ink are ordinarily provided in the ink jet printers in order to prevent such defects, but the ink remaining in the mechanisms is dried to be thickened and solidified in some cases, leading to a failure in normal cleaning operation. These problems tend to occur when the apparatus is at rest for a long period of time. Although (1) a method of cleaning an ink flow passage by using a cleaning liquid when the defect occurs, (2) a method of substituting the ink with the maintenance liquid in advance of a rest when the apparatus is scheduled to be rest for a long time, and the like have been proposed as countermeasures against the problems, the effect depends greatly on performance of the cleaning liquid or the maintenance liquid used in each of the methods.
Examples of the cleaning liquid or the maintenance liquid include a maintenance liquid comprising polyvalent alcohol, monovalent alcohol, and water (JP-B-6-8437); a maintenance liquid comprising monovalent alcohol, a negative ion surfactant, and water (JP-B-8-30200); a cleaning liquid improved in antifungal/antibacterial effect by containing an isothiazolone compound, (JP-A-4-261476); a cleaning liquid improved in antifoaming properties by containing a silicon antifoaming agent (JP-A-2000-328093); a maintenance liquid of pH 8 to 11 when a specific crosslinking ink is used (JP-A-2000-109733); a cleaning liquid comprising a surfactant (JP-A-11-263021, JP-A-11-263022); a cleaning liquid comprising a water-soluble salt of hydroxycarboxylic acid, limonene, and a surfactant (JP-A-2002-105500); and the like.
However, cleaning properties of the above cleaning liquids or maintenance liquids are insufficient in many cases due to the recent tendency of increase in colorant content in the ink mentioned above, and, as a result, there have been cases where serious reliability problems such as unstable discharge and nozzle clogging are caused. Particularly, in the pigment ink using a pigment as the colorant, the colorant (pigment) is present in the ink in the dispersed state, not in the dissolved state, and, therefore, when the pigment dispersion particles are aggregated by thickening or solidifying due to the ink drying, the cleaning liquids and the maintenance liquids are sometime insufficient for re-dispersion, thereby making the cleaning remarkably difficult.
Consequently, a maintenance liquid excellent in cleaning properties and usable for existing ink jet printers has been in demand.